Check valves are valves that allow fluid flow in one direction there through and prevent flow in the opposite direction. They are widely used in a range of applications, for example in air conditioning systems, for example in aircraft air conditioning systems.
Check valves commonly include one or more valve elements or flappers located at an opening in a valve housing. The flappers are hingedly supported on a hinge pin mounted to the valve housing for rotation between a closed position in which they lie across and close the opening, preventing fluid flow through the opening in one direction and an open position in which, under the pressure of a fluid (gas or liquid) on one side of the check valve, the flappers rotate from their closed positions so as to allow the fluid to flow through the valve in the opposite direction. Washers are usually provided on the hinge pin in order to assist in locating the flappers on the hinge pin.
Typical check valves also often have one or more physical stops, which limit the angle to which the flappers may open. When the flappers move from the closed to the open position, the flappers hit the stop or stops, thereby preventing the flappers from opening further. An example of such a stop is disclosed in U.S. Pat. No. 8,181,669.